This invention relates to semiconductor devices and methods. The invention has particularly advantageous application to III-V semiconductor light emitting devices, including semiconductor lasers and semiconductor light emitting diodes (LEDs).
In many semiconductor devices, there is a substantial volume of both n-type semiconductor material (that is, semiconductor doped with donor impurities so that electrons are majority carriers) and p-type semiconductor material (that is, semiconductor doped with acceptor impurities so that holes shortage of valence electrons! are majority carriers). In III-V semiconductor light emitting devices (e.g. lasers or LEDs), an active region can be disposed between n-type and p-type semiconductor regions. Upon application of an electrical potential, holes entering the active region from the p-type semiconductor material recombine with electrons entering the active region from the n-type semiconductor material, and photons are emitted.
In several respects, p-type material is more difficult to work with than n-type material, and tends to be operationally inferior to corresponding n-type material with regard to carrier mobility and overall electrical efficiency. Accordingly, it is often desirable to favor the use of n-type semiconductor material in the fabrication of semiconductor devices such as III-V light emitting devices. However, even though the substrate and a fractional majority of the semiconductor volume in such devices may be n-type semiconductor or undoped semiconductor, a substantial amount of p-type material is generally considered necessary as a source of hole current in various semiconductor devices. As described further hereinbelow, the disadvantages of employing p-type material in certain devices is even more pronounced when currents must travel laterally through p-type layers in planar devices.
It is among the objects of the present invention to improve semiconductor devices and methods by reducing the amount of p-type material that is needed in certain applications.